Fluid secretion by airway epithelium is important for normal lung development, mucocilliary clearance, and in disease processes such as asthma or cystic fibrosis. This grant is designed to study the controls of ion transport across airway epithelium during fetal development using electrophysiological, morphological, and genetic approaches. The specific aims are as follows: 1) To establish and characterize primary cell cultures of tracheal epithelium from rabbit and human fetuses of different gestational periods; 2) To search for molecules that regulate fluid transport during the transition from fetal to adult life; and 3) To study the signal transduction processes between cell surface receptors and ion channels in fetal tissues and to contrast the fetal with adult mechanisms.